Various MRI contrast agents have been developed for cellular MR imaging over the past few years. In general most contrast agents used for cell labeling are superparamagnetic iron oxide nanoparticles (SPIO) that result in T2 and T2 shortening of the surrounding tissues and hypointense regions on T2 weighted MRI. Paramagnetic contrast agents based on gadolinium can be used to label cells. Multifunctional fluorescent and SPIO nanoparticle contrast agents provides the ability to track labeled cells with cellular MRI and fluorescent microscopy. Several groups have reported functionalization of dextran coated SPION but not with a simple approach. We have developed a simple oxidation approach was used to introduce functional groups onto dextran coated SPION allowing for the reaction of the nanoparticles with several different fluorescent dyes. The fluorescent SPION were stable and successfully used for cell labeling. HeLa cells and mesenchymal stem cells were labeled with fluorescent dextran coated SPION such as fluorescent ferumoxides protamine sulfate complexes (FLUO FEPro) and quantitative cellular iron incorporation was similar to what was reported without fluorescent tag. FLUO FEPro labeled cells showed stronger fluorescent images confirming successful fluorescent dye conjugation onto dextran coated SPION. We have also systematically investigated a complex formation of negatively charged fluorescent (FL) SPION and positively charged peptide and derived a general complex theory to predict the complex formation. By conjugating Texas Red (Texas) dextran to SPION, we labeled stem cells via the complex formation and compared the labeling efficiency of these fluorescent SPION agents. We also evaluated multimodal nanoparticles labeled stem cells by fluorescent microscopy and MRI. Furthermore, we tracked labeled human mesenchymal stem cells in flank tumor nude mouse model by in vivo fluorescent and MR imaging.